1990 Jetta Idle/Running Issue...URGENT

Sounds like the idle throttle position switch is not working (if you have one, not sure what type fuel injection Canada got in 1990). The idle switch is at the bottom side of the throttle body, and there is another switch on top, the wide open throttle switch. The typical failure mode is that the plunger falls off the switch. I believe the WOT and the idle switches were wired in parallel in 1990, check if the connector has two or three pins. If it has two pins (= the two switches are wired in parallel), the test is very simple. Start the car, then get under the hood and manually depress the WOT switch. If this clears up the problem, the idle switch is at fault.

The dealer will sell you only the set of two switches (idle and WOT with the wring and connector. It will set you back over $100. You can fairly easily find the part at junk yards as well. To make things easy, look for the one with the same connector that you already have (2 or 3 pin). I needed 3-pin, but was not able to find it. No biggie, the switches are the same, so I just needed to do some soldering.

It is k>

Check your large boot to the air flow box. Maybe it is loose or cracked. Did you check the ground wires at either the intake manifold or the coolant pipe on the cylinder head. I usually check the FI wiring from the ECM harness plug at the ECM. :-) I have seen bad air flow boxes too! Is the timing done per Bentley's instructions? Did you check the timing belt timing? Check or plug most vacuum hoses to see if there is any change in your idle.

good luck too!

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Dave:

That is what's driving me nuts...everything is spot on where it should be....but I can't find a single thing to fault....grrrrrr :-s

Thanks,

Peter

IIRC, they are wired in parallel. I have the specs here somewhere on a resistance threshold in the switch but it's early and I have had a coffe.

Pete, I second the switch. In fact, upon experiencing similar problem in my '89 (Digifant), I drove around for a couple days with the connector bridged with a paper clip. Last year, the switches went for CDN~$70.

Good Luck, Darryl.

Get out that Bentley and do the component checks from the ECM harness plug. It makes it relatively easy to check from there. ;-) Did you try unpluggin the ISV and see what happens? I have seen defective ISVs cause similar problems. Got a used KNOWN GOOD one to try? later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Digifant II and therefore it should have one.